I've been trying to find a way to keep my system clone drive unmounted when not actively used. If for no other reason than to keep it spun down to reduce noise, power, and heat.

I tried to use the before/after scripts - a before would mount the drive and check a token file on it to verify that it's the expected target volume. The after script unmounts it. The problem is that SD! needs the drive mounted when it starts. My scheme works if I unmount the drive after SD! is started; this is okay when working manually but prevents using the scheduler.